1. Field of the Invention
The present application relates to an over-current protection device, and more particularly to a thin-type over-current protection device.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
Over-current protection devices are used for protecting circuitries from damage caused by over-heat, or over-current. An over-current protection device usually contains two electrodes and a resistive material disposed therebetween. The resistive material has positive temperature coefficient (PTC) characteristic that the resistance thereof remains extremely low at room temperature and instantaneously increases to thousand times when the temperature reaches a critical temperature or the circuit has over-current, so as to suppress over-current and protect the cell or the circuit device. When the resistive material gets back to the room temperature or over-current no longer exists, the over-current protection device returns to be of low resistance and as a consequence the circuitry again operate normally. In view of the reusable property, the PTC over-current protection devices can replace traditional fuses, and have been widely applied to high density circuits.
Electronic apparatuses are being made smaller. Therefore, it has to extremely restrict the sizes or thicknesses of active and passive devices in the electronic apparatus. According to cellular phone design, an over-current protection device usually is secured to a protective circuit module (PCM) board. The external electrodes connecting to the over-current protection device occupy a certain space, and therefore the over-current protection device has to be made thinner.
The over-current protection devices usually contain two stacked PTC devices connected in parallel in an attempt to lower the resistance of the over-current protection device. In FIG. 1, an over-current protection device 10 comprises two PTC devices 1 and 2. Each of the PTC devices 1 and 2 comprises metal foils 12a, 12b and a PTC material layer 11 disposed therebetween. The metal foils 12a of the PTC devices 1 and 2 are electrically connected to first electrodes 15 through a conductive connecting member 13, whereas the metal foils 12b are electrically connected to second electrodes 16 through a conductive connecting member 14. The metal foils 12a, 12b and the electrodes 15 and 16 are isolated by insulation layers 18. On the top and bottom surfaces of the device 10, solder masks 17 are formed between the electrodes 15 and the electrodes 16. Because the PTC device 1 and the PTC device 2 are connected in parallel the resistance of the over-current protection device 10 can decrease to meet the low-resistance requirement. However, the over-current protection device containing two stacked PTC devices is usually thick, resulting in difficulty to obtain a thinner structure.